1. Field of the Invention
The present invention relates to a centrifugal dryer for the separation of pellet-like substances from process water, comprising a housing, a rotor arranged in the housing and a screen surrounding the rotor at the peripheral side, with the screen having at least one porous screen member which is placed in an arcuate manner around at least one screen carrier hoop and is releasably fastened thereto.
2. Description of the Related Art
Plastic pellets which are manufactured by underwater pelletizing are continuously separated from the process water of the pelletizer system by centrifugal dryers connected downstream of the underwater pelletizers. Such centrifugal dryers, which can optionally also be used for the separation of other pellet-like substances from a corresponding fluid, usually have a rotor which stands upright, which is rotationally driven about an upright rotor axis and conveys the pellets or the pellet-water mixture from the bottom to the top by means of usually bucket-like conveying members, with the mixture being thrown radially outwardly. In this process, the pellets are retained in the screen surrounding the rotor, while the water or the corresponding fluid can pass through the porous screen members and can run off outside the screen.
Depending on the pellet size, sealing problems occur at the screens in this process. In this respect, seam points between individual screen members of which the screen is made up are in particular critical, as well as connection points between the screen members and connection bodies such as inlet stubs, outlet stubs and the like. There is also the fact in this respect that the screens must be cleaned and/or replaced regularly so that it is necessary to fasten the individual screen members releasably to the screen carrier, which is normally made up of a plurality of screen carrier hoops, so that the screen members can be removed, cleaned and replaced as necessary. The corresponding seam and connection points are in this respect particularly prone to sealing problems.
Usually, in this respect, flexible, bendable, board-like or plate-like screen members are used which can be placed around the screen carrier hoops in an arcuate or drum-jacket-like manner. The screen members have at their axially extending ends, which are adjacent in the position placed around the screen carrier hoops in the manner of a hoop, corresponding holding pieces, for example in the form of angle pieces or holding flanges, which are usually welded firmly to the usually metallic screen members or are optionally also clamped tight and then fixed for the purpose of the fastening of the screen members to one another. For example, U.S. Pat. No. 6,467,188, U.S. Pat. No. 6,505,416 or U.S. Pat. No. 6,438,866 show such cylindrical screens of centrifugal dryers in which screen members which are planar per se are first rolled up cylindrically and holding pieces are welded tight to the rims of the screen members which are then drawn together by screw-like clamping members. A centrifugal dryer for pellets is furthermore known from DE 43 30 078 A1 in which the screen is made up of two half-cylindrical shells. Each of the shell-like screen members is in this connection enclosed at its rims by a hoop-iron-like, belt-like frame section to which the actual screen member is welded tight. Two oppositely disposed frame section limbs are in this respect arched in the shape of a semi-circular arc so that the screen member is given a semi-cylindrical shell shape overall. The two half-screen shells are in this respect pivotally connected to one another in the manner of a hinge at two longitudinal-side frame sections so that the screen can be folded open.
Such screen constructions are capable of improvement in a variety of respects. On the one hand, they are relatively complex and/or expensive to manufacture since care must be taken that the screen members themselves are not deformed on the welding tight of the holding members at the screen member rims. If nevertheless welding deformation occurs, sealing problems arise. On the other hand, the screen members can only be rolled forward with difficulty, in particular when very stiff screen members have to be used for corresponding applications. The assembly and disassembly of the screen members is hereby made correspondingly more difficult.
Furthermore, screens made in this manner have little variability. If, for example, connection parts such as supply shafts or lead-off shafts should be connected to the screen at the periphery which communicate through the screen with the screen interior, the holding members or frame sections welded tight to the screen members are occasionally in the way. In addition, ultimately only one hole can be cut exactly to size in the screen to connect a supply shaft, for example.